既然这是一个重复的问题，我将提出一个完整的解决方案。这种
PairStream类型默认情况下是普通对象周围的简单包装器
Stream（尽管可以是
interface，也可以选择）。
它着重于提供方便的中间体操作和不能由调用的方法之一可以容易地进行这些终端的操作
keys()，
values()或
entries()返回到常规的单元素
Stream和连锁的终端操作。因此，例如，这
PairStream.from(map).filterValue(predicate).keys().findAny()是获取映射值与谓词匹配的键的直接方法。
filterValue是一种方便的中间操作，
keys转回到
Stream允许对键进行任意终端操作的普通操作。
一些例子
Map<String,Integer> m=new HashMap<>(); m.put("foo", 5); m.put("bar", 7); m.put("baz", 42); // {b=49, f=5} Map<Character,Integer> m2=PairStream.from(m) .mapKey(s->s.charAt(0)) .toMap(Integer::sum); // foo bar String str=PairStream.from(m) .filterValue(i->i<30) .keys().sorted(Comparator.reverseOrder()) .collect(Collectors.joining(" ")); Map<String,Integer> map=new HashMap<>(); map.put("muhv~", 26); map.put("kfool", 3); String str = PairStream.from(map) .sortedByValue(Comparator.naturalOrder()) .flatMapToInt((s,i)->s.prePoints().map(c->c^i)) .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append) .toString();这是完整的类（我尚未测试所有操作，但是大多数操作都是简单明了的）：
import java.util.*;import java.util.function.*;import java.util.stream.*;public interface PairStream<K,V> { static <K,V> PairStream<K,V> from(Map<K,V> map) { return from(map.entrySet().stream()); } static <K,V> PairStream<K,V> from(Stream<Map.Entry<K,V>> s) { return ()->s; } static <K,V> PairStream<K,V> from(Stream<K> s, Function<? super K, ? extends V> f) { return ()->s.map(k->new AbstractMap.SimpleImmutableEntry<>(k, f.apply(k))); } default PairStream<K,V> distinct() { return from(entries().distinct()); } default PairStream<K,V> peek(BiConsumer<? super K, ? super V> action) { return from(entries().peek(e->action.accept(e.getKey(), e.getValue()))); } default PairStream<K,V> skip(long n) { return from(entries().skip(n)); } default PairStream<K,V> limit(long maxSize) { return from(entries().limit(maxSize)); } default PairStream<K,V> filterKey(Predicate<? super K> mapper) { return from(entries().filter(e->mapper.test(e.getKey()))); } default PairStream<K,V> filterValue(Predicate<? super V> mapper) { return from(entries().filter(e->mapper.test(e.getValue()))); } default PairStream<K,V> filter(BiPredicate<? super K, ? super V> mapper) { return from(entries().filter(e->mapper.test(e.getKey(), e.getValue()))); } default <R> PairStream<R,V> mapKey(Function<? super K,? extends R> mapper) { return from(entries().map(e->new AbstractMap.SimpleImmutableEntry<>( mapper.apply(e.getKey()), e.getValue() ))); } default <R> PairStream<K,R> mapValue(Function<? super V,? extends R> mapper) { return from(entries().map(e->new AbstractMap.SimpleImmutableEntry<>( e.getKey(), mapper.apply(e.getValue()) ))); } default <R> Stream<R> map(BiFunction<? super K, ? super V,? extends R> mapper) { return entries().map(e->mapper.apply(e.getKey(), e.getValue())); } default DoubleStream mapToDouble(ToDoubleBiFunction<? super K, ? super V> mapper) { return entries().mapToDouble(e->mapper.applyAsDouble(e.getKey(), e.getValue())); } default IntStream mapToInt(ToIntBiFunction<? super K, ? super V> mapper) { return entries().mapToInt(e->mapper.applyAsInt(e.getKey(), e.getValue())); } default LongStream mapToLong(ToLongBiFunction<? super K, ? super V> mapper) { return entries().mapToLong(e->mapper.applyAsLong(e.getKey(), e.getValue())); } default <RK,RV> PairStream<RK,RV> flatMap( BiFunction<? super K, ? super V,? extends PairStream<RK,RV>> mapper) { return from(entries().flatMap( e->mapper.apply(e.getKey(), e.getValue()).entries())); } default <R> Stream<R> flatMapToObj( BiFunction<? super K, ? super V,? extends Stream<R>> mapper) { return entries().flatMap(e->mapper.apply(e.getKey(), e.getValue())); } default DoubleStream flatMapToDouble( BiFunction<? super K, ? super V,? extends DoubleStream> mapper) { return entries().flatMapToDouble(e->mapper.apply(e.getKey(), e.getValue())); } default IntStream flatMapToInt( BiFunction<? super K, ? super V,? extends IntStream> mapper) { return entries().flatMapToInt(e->mapper.apply(e.getKey(), e.getValue())); } default LongStream flatMapToLong( BiFunction<? super K, ? super V,? extends LongStream> mapper) { return entries().flatMapToLong(e->mapper.apply(e.getKey(), e.getValue())); } default PairStream<K,V> sortedByKey(Comparator<? super K> comparator) { return from(entries().sorted(Map.Entry.comparingByKey(comparator))); } default PairStream<K,V> sortedByValue(Comparator<? super V> comparator) { return from(entries().sorted(Map.Entry.comparingByValue(comparator))); } default boolean allMatch(BiPredicate<? super K,? super V> predicate) { return entries().allMatch(e->predicate.test(e.getKey(), e.getValue())); } default boolean anyMatch(BiPredicate<? super K,? super V> predicate) { return entries().anyMatch(e->predicate.test(e.getKey(), e.getValue())); } default boolean noneMatch(BiPredicate<? super K,? super V> predicate) { return entries().noneMatch(e->predicate.test(e.getKey(), e.getValue())); } default long count() { return entries().count(); } Stream<Map.Entry<K,V>> entries(); default Stream<K> keys() { return entries().map(Map.Entry::getKey); } default Stream<V> values() { return entries().map(Map.Entry::getValue); } default Optional<Map.Entry<K,V>> maxByKey(Comparator<? super K> comparator) { return entries().max(Map.Entry.comparingByKey(comparator)); } default Optional<Map.Entry<K,V>> maxByValue(Comparator<? super V> comparator) { return entries().max(Map.Entry.comparingByValue(comparator)); } default Optional<Map.Entry<K,V>> minByKey(Comparator<? super K> comparator) { return entries().min(Map.Entry.comparingByKey(comparator)); } default Optional<Map.Entry<K,V>> minByValue(Comparator<? super V> comparator) { return entries().min(Map.Entry.comparingByValue(comparator)); } default void forEach(BiConsumer<? super K, ? super V> action) { entries().forEach(e->action.accept(e.getKey(), e.getValue())); } default void forEachOrdered(BiConsumer<? super K, ? super V> action) { entries().forEachOrdered(e->action.accept(e.getKey(), e.getValue())); } default Map<K,V> toMap() { return entries().collect( Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); } default Map<K,V> toMap(BinaryOperator<V> valAccum) { return entries().collect( Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, valAccum)); }}
